perf(cpus): inline cpu_rev_var checks
We strive to apply errata as close to reset as possible with as few
things enabled as possible. Importantly, the I-cache will not be
enabled. This means that repeated branches to these tiny functions must
be re-fetched all the way from memory each time which has glacial speed.
Cores are allowed to fetch things ahead of time though as long as
execution is fairly linear. So we can trade a little bit of space (3 to
7 instructions per erratum) to keep things linear and not have to go to
memory.
While we're at it, optimise the the cpu_rev_var_{ls, hs, range}
functions to take up less space. Dropping the moves allows for a bit of
assembly magic that produces the same result in 2 and 3 instructions
respectively.
Change-Id: I51608352f23b2244ea7a99e76c10892d257f12bf
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/lib/cpus/aarch64/cpu_helpers.S b/lib/cpus/aarch64/cpu_helpers.S
index 0f9a3b8..537f715 100644
--- a/lib/cpus/aarch64/cpu_helpers.S
+++ b/lib/cpus/aarch64/cpu_helpers.S
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2014-2023, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2025, Arm Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
@@ -237,59 +237,6 @@
endfunc cpu_get_rev_var
/*
- * Compare the CPU's revision-variant (x0) with a given value (x1), for errata
- * application purposes. If the revision-variant is less than or same as a given
- * value, indicates that errata applies; otherwise not.
- *
- * Shall clobber: x0-x3
- */
- .globl cpu_rev_var_ls
-func cpu_rev_var_ls
- mov x2, #ERRATA_APPLIES
- mov x3, #ERRATA_NOT_APPLIES
- cmp x0, x1
- csel x0, x2, x3, ls
- ret
-endfunc cpu_rev_var_ls
-
-/*
- * Compare the CPU's revision-variant (x0) with a given value (x1), for errata
- * application purposes. If the revision-variant is higher than or same as a
- * given value, indicates that errata applies; otherwise not.
- *
- * Shall clobber: x0-x3
- */
- .globl cpu_rev_var_hs
-func cpu_rev_var_hs
- mov x2, #ERRATA_APPLIES
- mov x3, #ERRATA_NOT_APPLIES
- cmp x0, x1
- csel x0, x2, x3, hs
- ret
-endfunc cpu_rev_var_hs
-
-/*
- * Compare the CPU's revision-variant (x0) with a given range (x1 - x2), for errata
- * application purposes. If the revision-variant is between or includes the given
- * values, this indicates that errata applies; otherwise not.
- *
- * Shall clobber: x0-x4
- */
- .globl cpu_rev_var_range
-func cpu_rev_var_range
- mov x3, #ERRATA_APPLIES
- mov x4, #ERRATA_NOT_APPLIES
- cmp x0, x1
- csel x1, x3, x4, hs
- cbz x1, 1f
- cmp x0, x2
- csel x1, x3, x4, ls
-1:
- mov x0, x1
- ret
-endfunc cpu_rev_var_range
-
-/*
* int check_wa_cve_2017_5715(void);
*
* This function returns: